The present invention relates to apparatus for leaching constituents from mineral materials and particularly relates to apparatus for distributing a leaching solution in a vessel containing mineral ores and controlling the outflow of slurry, all as part of a countercurrent continuous process for recovering valuable minerals from the ore.
Leaching systems are well known for the recovery of valuable metals from mineral ores. For example, gold or silver has been extracted from ores by leaching the ores with alkaline cyanide solution and oxygen in a continuous process, as contrasted with a batch process. The mineral-containing ore is generally crushed and disposed in a slurry through which the treatment solution, i.e., the cyanide solution, is passed countercurrent to the flow of the slurry. The pregnant leaching solution is usually removed from the top of the vessel and passed through a carbon adsorber, the valuable minerals being subsequently removed from the loaded carbon material.
In prior systems, leaching solution enters the lower end of the tank through the distribution nozzles of a rotary distribution arm. These nozzles, however, are prone to clog and plug, for example, by entry of the slurry from the tank into the nozzles. Plugging of the nozzles deleteriously affects the distribution of the treatment solution in the slurry. That problem and various other problems associated with that type of leaching system were attempted to be solved by an improved system disclosed in U.S. Pat. No. 4,807,854 of common assignee herewith. In that system, a pair of vertically spaced distribution arms are disposed in the vessel, one for distributing a washing solution in the slurry and the other for distributing a cyanide solution into the slurry. Discrete flow paths for the delivery of each of the two different solutions into the slurry through the respective arms are provided. Particularly, each aperture or nozzle in each arm had associated with it a tubing for conveying the solution through a central hub and into the arm. Each aperture and flow path had a flow control valve associated therewith.
As much as that system constituted an improvement over the prior leaching systems, it also imposed certain mechanical problems. For example, problems occurred with respect to the mechanical seals. Also, the need to provide independent tubing to supply each of the apertures through the distribution arm and the rotating central hub of the distribution system provided a relatively mechanically complex system which increased costs. Additionally, a portion of the pregnant leaching solution washed out of the vessel with the slurry, whereby the dissolved mineral could not be recovered. That is, such additional concern involves the washing of the dissolved gold out of the vessel with the slurry rather than flowing the valuable mineral in solution upwardly toward the collection point at the top of the vessel.
According to the present invention, there is provided an apparatus for leaching mineral ores in a continuous countercurrent process to remove the valuable mineral constituents contained in the ore and which reduces the mechanical problems associated with prior systems, as well as improves the distribution of the cyanide leaching solution to minimize the flow of dissolved gold with the slurry and maximize recovery of the pregnant leaching solution. While the apparatus and methods according to the present invention are particularly applicable to the removal of metals, such as gold and silver, from metal-bearing ores containing such metals, they may also be adaptable to other processes, such as the removal of pyritic, organic and sulfite sulfa compounds present in solid carbonaceous fuel of the coal or coke type.
According to one aspect of the present invention, there is provided a vertically disposed treatment vessel for containing a slurry, preferably comprised of mineral-bearing ores, such as gold or silver ore. A slurry outlet is provided at the bottom wall of the vessel and a pump having, for example, auger-type blades, is disposed in the outlet for drawing slurry from the vessel. The pump is also a centrifugal pump for pumping the slurry from the vessel in a radial direction. In conjunction with the pump, there is also provided an inclined wall which extends from the slurry outlet, inclining upwardly toward the outer walls of the vessel to define with the bottom wall of the vessel at least one compartment for receiving treatment solution. Particularly, the inclined wall is provided with a series of apertures and the bottom wall of the vessel is provided with an inlet for the treatment solution, e.g., cyanide solution. With this structure, the cyanide solution is introduced into the compartment through the bottom wall of the vessel and into the slurry through the apertures in the inclined wall. Thus, the introduction of the cyanide solution into the slurry is by way of a static structure which involves no moving parts. Additionally, the apertures can be arranged as desired in the inclined wall to achieve the desired distribution of treatment solution in the slurry. Also, by inclining the wall, the slurry is directed downwardly toward the outlet opening and the pump to facilitate slurry removal.
In a preferred form of the present invention, the compartment below the inclined wall is divided into defined volumes or chambers each provided with a separate inlet and flow control valve for flowing the treatment solution into the chamber and through the apertures associated with that chamber into the slurry. Many different configurations of chambers may be provided. For example, the compartment below the inclined wall can be segregated into two or more concentric chambers, each with its own treatment solution inlet and flow control valve. In another embodiment, the volume below the inclined wall can be divided into circumferentially-spaced chambers, for example, by extending radially from the vertical axis of the vessel and walls forming quadrants. Each quadrant is provided with a separate treatment solution inlet and associated flow control valve. In a still further embodiment, the compartment below the inclined wall is divided into both radially spaced concentric and circumferentially spaced chambers, each being provided with its own inlet and control valve for the treatment solution. In this manner, the distribution of the treatment solution in the slurry is closely controlled such that the flow of the pregnant solution containing the dissolved gold toward the top of the vessel and the collection point therefor is facilitated. While certain of the treatment solution may flow upwardly through the apertures into contact with the slurry and then immediately downwardly along the inclined wall toward the slurry outlet, this loss in treatment solution contains only minimal dissolved gold and is offset by the gain in dissolved gold flowing upwardly in the PG,7 vessel toward the collection point as a result of the unique treatment solution distribution hereof.
In a preferred embodiment according to the present invention, there is provided apparatus for treating slurries comprising an upright vessel for containing the slurry. Means defining an inlet for flowing a treatment solution into the vessel and into the slurry are provided and include an inclined wall adjacent the bottom of the vessel having a plurality of apertures therethrough, the wall being inclined toward the outlet to deliver slurry thereto. Additional means defining an outlet for the slurry adjacent the bottom of the vessel are also provided. A pump is disposed adjacent the outlet to pump slurry from the vessel through the outlet.
In a further preferred embodiment according to the present invention, there is provided apparatus for treating slurries comprising an upright vessel for containing the slurry. Means defining an inlet for flowing a treatment solution into the vessel and into the slurry are provided and include an inclined wall adjacent the bottom of the vessel having a plurality of apertures therethrough. Additional means defining an outlet for the slurry adjacent the bottom of the vessel are also provided. The inlet defining means includes means defining a plurality of discrete chambers below the inclined wall, with each chamber lying in communication with at least an aperture and each chamber having a discrete treatment solution inlet.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus for improving the distribution of the treatment solution in a vessel to enhance the flow of the valuable mineral constituent in solution by using a static mechanical distribution structure, and simultaneously facilitating the flow of slurry from the vessel.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.